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Typically, primary (female) piles are cast in situ, leaving space in between them. This is followed by secondary (male) piles being cut into the primary piles to form a continuous wall, generally with a typical interlock of around 150 mm.

Depending on the composition of the secondary piles, it can be hard/soft, hard/firm or hard/hard:

Hard/soft uses a ‘soft’ cement-bentonite mix (typically 1 N/mm2) for the primary pile, and this is usually unreinforced. This composition generally does not provide full water-tightness.

Hard/hard is similar to hard/firm but the primary piles are typically of higher-strength concrete and may be reinforced. This can provide an alternative to diaphragm wall construction.

The advantages of secant pile walls are that, compared to sheet piling methods, they can provide greater wallstiffness. They are also capable of being installed in low headroom and in difficult ground conditions.

The disadvantages are that vertical tolerances may be difficult to achieve for deep piles, as is total waterproofing in the joints between piles. They will also generally cost more than sheet piles.